This bug occurs in 692. I am not sure about 697. To see this bug, create a screen with a Patra level 1 or 2 (the one that has the kids go in a circle around it that can expand). Play the screen, and lure the patra towards the edge of the screen. When it expands, if one of the mini patra kids flys off the screen, it won't come back on. This probably has something to do with the enemies leaving screen bug that Joe123 reported.
Patra kid bug (692)
This has been fixed in the next build.